A. Field of the Invention
The field of the present invention relates generally to roof systems, particularly metal roof installations, that are configured to facilitate air circulation between roof layers and vent the heated air from the roof. Even more particularly, this invention relates to such roof venting systems that are configured to provide environmental benefits, such as improved interior air circulation and the production of hot water and electricity.
B. Background
Many structures utilize metal roof systems to protect the interior of the structure from exposure to the elements, including sun, rain, snow and the like. Metal roofs are beneficially utilized on metal, brick, wood and various other structures. Generally, the structure is built with interior columns that support a series of rafters or beams attached at the top of the columns. The roof rafters or beams are typically attached in a sloped manner with a ridge at the top or, particularly with commercial buildings, at one end of the structure to provide positive downward drainage. Spanning the rafters or beams are a series of light gauge metal Z-shaped or C-shaped structural members commonly referred to as purlins. The purlins generally run perpendicular to the rafters or beams and are configured to be in a spaced apart relationship to each other provide structural support for the overlying metal roof system.
One well known and commonly utilized metal roof system for sloped roofs comprises a decking attached to the purlins and a plurality of metal panels attached to the decking with a thermal barrier disposed between the decking and metal panels. The decking material is attached with screws or bolts directly to the purlins that are attached to the roof rafters or beams. Most often, but not exclusively, the decking consists of a plurality of wooden panels, such as plywood, spaced side-by-side on top of the purlins. In many areas of the United States, the thermal and waterproof barrier is placed over the decking material to resist the flow of water, either from rain or snow, into the structure and to provide some degree of insulating effect for the interior of the structure. One common type of thermal barrier comprises roofing (i.e, felt) paper with a plastic covering over the roofing paper. The uppermost part of the roof, the metal panels, are attached to the decking on top of the thermal barrier. A very common type of metal panel utilized for metal roofs is the corrugated steel sheet having a plurality of spaced apart and parallel, alternating ribs and valleys. One type of such system is referred to as standing seem metal roofing, which utilizes metal roof panels having a standing rib on one side of the roof panel and a hook rib on the opposite side of the panel. The hook rib of one panel is placed over the standing rib of the adjacent panel and a machine is utilized to seam or join together the two adjacent panels by jointly folding over the hook rib and standing rib. Although the rib configuration (i.e., the shape and size) varies considerably among the many manufacturers of corrugated panels, the valleys are generally flat to form a lower plane that is spaced apart from the top of the ribs. Threaded screws are typically used to attach the metal panels to the underlying decking.
The above-described roofing system is generally sufficient to obtain a relatively strong, lightweight and weather resistant roof to protect the interior and building components of a structure. A common and well known problem with all metal roofs, however, results from the high thermal conductivity of the metal material used for the roofing. During cold weather or when snow is on the roof, the metal roof components will contract. When there is sunshine, even during cold days, the sun will heat up the upper metal panels and the air trapped between the metal panels and the decking. The heretofore standard configuration for metal roofs results in thermal expansion and contraction (i.e., thermal flexing) of the roof in response to temperature changes during the day and through the seasons. In areas of the United States where colder temperatures and/or snow conditions are common in the winter months, the thermal flexing of the roofing material is even more pronounced (particularly on the side of the roof that faces the sun). One well known result of this thermal flexing is that the threaded metal screws will back partially or completely out from the decking to which they were attached. The heating and cooling of the interior of the structure worsens this problem by creating back pressure that helps work the screw out. In addition to the obvious problem of reducing the structural integrity of the roof system, the backing out of the screws creates a conduit for moisture to enter into the space between the metal panels and the decking. Once moisture enters this area, it begins to result in the rotting of the thermal barrier and then the underlying decking, thereby damaging the roof and necessitating expensive repairs and/or retrofitting of the roof. Even without the backing out problem, moisture can build-up in between the metal panels and the decking due to the “sweating” of the metal panels from the temperature fluctuations of the air trapped therein.
Builders of structures having metal roofs have long known of the benefits of installing a vent along the roof ridge to vent out air from the attic or interior of the structure. Early vents were as simple as an open slot running along the entire length of the ridge. Later vents were developed to allow air to escape but prevent moisture and other elements from entering the interior of the structure. The ridge vents allow air to vent from the structure by convection airflow and by suction from wind blowing across the roof. Air vents added to the eave (or soffit) of the structure improved airflow by providing passive ventilation through the introduction of fresh ambient air into the attic or interior. As stale, hot air is withdrawn from the structure by convection and/or wind suction at the ridge vent, fresh ambient air is drawn into the attic or structure at the eave vent.
Other inventors have developed a variety of systems for the convection of air from structures having metal roofs. For instance, U.S. Pat. No. 5,765,329 to Huang describes roof venting system for metal roofs using two sets of corrugated metal sheets with spacers between the sheets to vent hot air to the atmosphere through a plurality of apertures in the corrugated sheets for improved heat radiation, heat insulation and the withdrawal of gasses from the interior space of the building. U.S. Pat. No. 5,826,383 to Garrison describes a roof venting system that utilizes ridge venting and eave venting to vent hot air from the interior of the building while preventing water, debris and pests from entering the interior of the building. U.S. Pat. No. 5,561,953 to Rotter describes a roof ridge ventilation system for metal roofs to allow vapors inside the building to vent out through an air permeable, resilient member located at the roof ridge. U.S. Pat. No. 5,367,848 to McConnohie describes a bracket for use to attach a new metal roof over the ribbed panels of an existing corrugated metal roof.
A metal roof system configured to solve the thermal flexing problems described above is set forth in U.S. Pat. No. 6,401,412 to Cooper (the '412 patent), one of the present inventors. The disclosure of the '412 Patent is incorporated herein by this reference. In summary, the roof system described in the '412 Patent comprises a lower wooden decking layer, an upper metal panel layer and a spacer disposed between the decking and metal panels. In certain parts of the United States it is advantageous to include a thermal barrier layer between the decking and the spacers to further protect the decking. The decking is generally attached to the roof rafters, or to purlins attached to the roof rafters, with the use of screws and the like, as are suitable for securely fastening the decking to the structure. Typically, the decking is made from a plurality of plywood panels laid side-by-side across the entire roof of the structure. The metal panels can comprise a plurality of corrugated metal sheets joined together side-by-side across the roof (i.e., standing seam roof system) and attached to the spacers on the decking utilizing metal screws or other fastening devices for securely fastening the metal panels to the spacer. The metal panels are joined to the spacers at the flat valleys.
In the preferred embodiment of the invention described in the '412 patent, the spacer comprises a shaped member, such as a z-shaped purlin, configured to have a generally planar top section to abut the planar surface formed by the flat valleys of the metal panels, a generally flat bottom section to abut the planar surface of the decking and a center section that vertically disposes the top and bottom sections in a spaced apart relationship. The bottom section of the spacer attaches to the decking or the rafters or purlins under the decking using the appropriate wood or metal screws. The metal panels attach to the top section of the spacer at the flat valley portions of the metal panels using metal screws or the like. The center section of the spacer includes one or more openings therein to form an airflow cavity between the decking and the metal panels. In the preferred embodiment, the center section has a plurality of openings sized and configured so as to not substantially reduce the strength and carrying capability of the spacer.
Although the roof system of the '412 Patent works well to increase air flow beneath the metal roof panels and reduce the effect of thermal changes on the roof system, an improved venting system that cooperates with such a roof installation is needed to further facilitate the circulation of air so as to better obtain the benefits therefrom. As well known in the art, many commercial roofs are configured to be generally flat, as opposed to the typical home roof having a centrally disposed ridge, with only a slight degree of incline from the top or high end to the bottom or low end. Most commercial roofs have a parapet wall around the outer edges of the roof that has one or more drainage openings therein on at least the sides and the lower end to drain water off the roof, generally to the ground below. Typically, the metal roof of commercial buildings extends from parapet to parapet.
As is well known in the building and roofing industries, many modern buildings are constructed with materials and are configured in a manner that is designed to provide environmental benefits for operation and use of the building. In fact, many buildings are evaluated on the environmental friendliness of the completed structure. With regard to roof systems, many building contractors and owners desire to have a “green roof” that, in addition to satisfying the usual structure protection requirements, utilizes improved materials and systems to reduce the cost of using the building (i.e., lower electricity consumption by reducing the requirements to heat and/or cool the building interior), which also benefits the environment through reduced generation of electricity by fossil fuels or other means. Examples of such materials and systems are well known and include the use of metal (i.e., recyclable) roof panels or shingles, solar panels mounted to the roof so as to directly produce electricity, roof mounted solar heated piping systems to produce hot water for pools and hot water supply systems, and roof coverings, coatings or insulation to better insulate the roof and reduce the summer heating or winter cooling effect thereon. Metal roofs also have the advantage of a relatively high strength-to-weight ratio, which reduce the stresses on the other structure components and allows metal roofing to be used to cover old roofing materials, which reduces the need to remove the old materials and dispose of them in landfills and other disposal sites. Piping systems are also known to divert heated water through the floor of the structure so as to reduce the need to heat the structure or cool water through the floor to reduce the need to cool the structure. To assist in characterizing and evaluating the environmental performance of different structures, the United States Green Building Council (the “USGBC”) developed a rating system to compare the environmental, economic, health and productivity performance of a “green building” to a conventional building. With this rating system, known as the Leadership in Energy & Environmental Design or (“LEED”), a building is evaluated with a checklist that allows the building to earn points or credits for meeting specific identified performance criteria and obtain a Leed certification level (i.e., silver, gold or platinum levels). In addition to the use of “green” materials and systems resulting in reduced operating costs for the building, a higher rating level can affect the availability of grants and/or other funding for the building. In general, the use of metal for the roof is known to contribute points toward the certification of a building as “green” under the above-mentioned standards.
In addition to providing a building that is more economical to operate, building contractors and owners generally desire to provide a structure that is healthy to live or work in. Unfortunately, for many people the interior of their home or office may not be that healthy of an environment due to the circulation of air through the building that carries dust, pollen or other allergens or pollutants. For these people specifically, and others in general, the interior air of the building in which they live or work is known to cause breathing, allergy and other health problems that can substantially reduce the quality and enjoyment of their lives. To address this concern, a number of homes, office buildings and other structures have been built with or modified to incorporate air filtration systems that are configured to remove or at least substantially reduce the dust, allergens, pollutants and other materials in the air being circulated in the building. A variety of different air filtration devices, including filter systems having HEPA or similar filters, are well known for use in cleaning the interior air of a building. Generally, these devices are placed in the stream of air coming into the building to remove the dust, allergens, pollutants or other materials therein so that a substantially clean stream of air can be circulated inside the building.
What is needed is an improved venting system for metal roof installations, particularly those utilized on commercial buildings and the like. It is particularly desirable to provide a venting system for metal roofs that is configured to cooperate with an air circulating/venting system, such as that described in the '412 Patent or which is otherwise utilized. The preferred venting system should be configured to more beneficially vent the air from between an upper layer of roofing material and the lower layer of roofing materials, such as between metal roof panels and the underlying wood sheeting, be relatively simple to install and not add substantially to the cost of the typical roof system. In an even more preferred system, a roof system is desired that utilizes the vented air for purposes of improving the air circulated to the interior of the building, providing hot water for use in or around the building and to provide a source of electricity for the building.